The present invention relates to a high-temperature member for use in a gas turbine. More particularly, the present invention relates to a high-temperature member formed from a cobalt-based alloy which is less subject to wear and damage due to vibrations generated by a running turbine.
A gas turbine generates, during its operation, continuous vibrations resulting from high-speed revolution of rotors and flows of combustion gas and compressed cooling air. This vibrational action causes wear and damage to high-temperature members constituting the gas turbine. Such wear and damage occur at the part with which each member is in contact by fitting. Since these gas turbine members are used at high temperatures, it is impracticable to supply their sliding parts with a lubricant (such as oil). In many cases they are used without lubrication. Under these circumstances, it is essential to make those members subject to vigorous vibrations from a wear resistant material. Existing high-temperature wear resistant materials are mostly composed of a cobalt—, iron—, or nickel-based alloy and hard particles of carbide or boride in a comparatively high ratio (say, several percent by volume or more).
The above-mentioned high-temperature wear resistant materials are poor in ductility because they contain a large number of hard particles. Consequently, they are hardly formed into a complex shape by machining or a sheet by rolling or pressing at room temperature. This means that they have limitations in the shape of members into which they are made or the manufacturing process by which they are made into members. On the other hand, it is common practice to coat the surface of members (by plasma spraying) with a wear resistant material containing hard particles. However, difficulties are often encountered in forming a perfect coating film on the inside of a member having an intricate shape. Cobalt-based wear resistant alloys (typified by stellite), which are commonly used for surface coating by overlaying or thermal spraying, also encounter difficulties in application to a complicated surface.
Cobalt-based alloys containing a less amount of hard carbide can be made into members in complex shape by cold working; however, such alloys are inevitably incomplete in wear resistance.